Office lighting constitutes almost 30% of the electrical consumption in buildings. As the cost and energy efficiency of light-emitting-diode (LED) light sources improve, they are becoming viable alternatives for fluorescent lamps, further offering the advantage of color control. It is recognized that lighting control strategies based on occupant presence information are very effective in reducing energy consumption. For example, in unoccupied areas the illumination may be dimmed or extinguished. Hence the design of green buildings may benefit from presence-adaptive lighting control systems.
It is known that active sensors, such as ultrasound based sensors, provide better detection than passive infrared sensors in large volumetric spaces. It is further known that active sensors are more sensitive than passive infrared sensors generally. An ultrasonic array sensor has been described in WO 2005/069698 for reliable presence sensing that, when interfaced with a lighting control system, provides reliable illumination rendering.
In accordance with WO 2005/069698, a light source illuminates a local area with light that is modulated to identify the local area. In response to detection of the modulated light, a wearable occupancy detector located in the local area radiates a signal identifying the local area. The radiated signal is received by a control unit that is in communication with the light source and is capable of controlling a lighting function of the light source. Occupancy detection in accordance with WO 2005/069698 does not depend on motion.